<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Promise链式调用_解决回调地狱</title>
</head>

<body>
  <form>
    <span>省份：</span>
    <select>
      <option class="province"></option>
    </select>
    <span>城市：</span>
    <select>
      <option class="city"></option>
    </select>
    <span>地区：</span>
    <select>
      <option class="area"></option>
    </select>
  </form>
  <script src="https://cdn.jsdelivr.net/npm/axios/dist/axios.min.js"></script>
  <script>
    /**
     * 目标：把回调函数嵌套代码，改成Promise链式调用结构
     * 需求：获取默认第一个省，第一个市，第一个地区并展示在下拉菜单中
    */
    let pname = ''
    // 1. 得到-获取省份Promise对象
    axios({url: 'http://hmajax.itheima.net/api/province'}).then(result => {
      pname = result.data.list[0]
      document.querySelector('.province').innerHTML = pname
      // 2. 得到-获取城市Promise对象
      return axios({url: 'http://hmajax.itheima.net/api/city', params: { pname }})
    }).then(result => {
      const cname = result.data.list[0]
      document.querySelector('.city').innerHTML = cname
      // 3. 得到-获取地区Promise对象
      return axios({url: 'http://hmajax.itheima.net/api/area', params: { pname, cname }})
    }).then(result => {
      console.log(result)
      const areaName = result.data.list[0]
      document.querySelector('.area').innerHTML = areaName
    })
  </script>
</body>

</html>